The use of stents within vessels, such as arterial vessels, is well known. Generally, devices of this type are inserted into a vessel to support the vessel wall, and thus prevent the wall from collapsing and occluding the vessel. Alternatively, in a procedure commonly referred to as vascular repaving, stents may be inserted into a weakened portion of a vessel to prevent internal pressure within the vessel from causing the vessel wall to rupture. Accordingly, stents may be useful whenever a vessel wall has become weakened (such as by disease) or when the vessel becomes clogged (such as by the buildup of plaque), or whenever surrounding tissue (such as a tumor) is applying pressure to the outside of a vessel which may cause the vessel to collapse.
The benefits associated with the use of stents has resulted, not surprisingly, in the increased use of stents to treat an ever increasing number of maladies. As a result, a wide variety of differing stent designs have been developed, each of which may be more, or less, appropriate for the treatment of a particular condition. A contributing factor to the proliferation of differing stent types has been the problematic conditions faced as part of the design and fabrication of a beneficial stent. For example, it is readily appreciated that the operational environment into which a stent is to be placed may vary widely from the idealized conditions of a laboratory. Specifically, the vessel into which the stent is to be placed may be curved or otherwise tortuous. In such cases, insertion of an inflexible stent may be undesirable or even impossible. This particular difficulty is often avoided by the use of a shorter stent, or even a series of shorter stents. In either case, however, the treatment may be complicated or the efficacy of the treatment may be reduced.
Tapered vessels present another aspect of stent design which can be of concern. Tapered vessels, are of course, not uncommon and may even occur in combination with the curved vessel discussed in the preceding section. In cases with tapered vessels, the use of a stent which cannot conform to the changing diameter of the vessel may be problematic. Once again, the use of a series of shorter stents is possible, but this necessarily complicates the course of treatment.
The particular treatment site may also subject the stent to a relatively large compressive load. In such cases the use of a stent which recoils under the load would be inappropriate. The solution for many cases of this type is the utilization of a stronger, or more robust, stent. The use of a stronger stent may not be possible, however, if the stent is required to provide a high degree of flexibility such as when placement within a curved or tapered vessel is required.
Practice has also shown that the use and placement of stents in small vessels is particularly difficult. More specifically, at present, most stents are designed to be delivered in an un-expanded state and then expanded, in-situ, to support the vessel at the target site. In small vessels (generally those with a diameter of less than three millimeters), there may not be adequate room to allow passage of the stent. This may be so even with the stent in its unexpanded state. The use of smaller stents is possible, but may in itself be difficult if the stent is not strong enough to support the intended compressive load.
In light of the above, it is an object of the present invention to provide a vascular stent which can be inserted into a vessel to support the vessel wall. Another object of the present invention is to provide a vascular stent which can withstand a relatively large compressive load without recoiling. Another object of the present invention is to provide a vascular stent which can be inserted into relatively small vessels. Still another object of the present invention is to provide a vascular stent which expands substantially iso-concentrically to more nearly replicate the original lumen of a vessel and can be utilized in a curved or tapered vascular segment. Yet another object of the present invention is to provide a stent which reliably stays in position in the vessel. Still another object of the present invention is to provide a vascular stent which is relatively easy to manufacture, simple to operate and comparatively cost effective.